Endotracheal tubes are commonly used during anesthesia and intensive care in order to support respiration of a human patient who may be unable to breathe without the use of mechanical breathing support devices. Endotracheal tubes may have electrodes on the surface thereof for performing laryngeal electromyography and monitoring the recurrent laryngeal nerve during medical procedures. These electrodes on the endotracheal tube, referred to as laryngeal surface electrodes, are currently used in various surgical procedures to provide monitoring of the electromyographic signals from the muscles of the vocal cords, or larynx. The electrical signal typically transmitted to the tissue and detected using electronic monitoring equipment is generally from about 10 microvolts to about 2 millivolts. This monitoring procedure allows the surgeon to intermittently stimulate the nerves, for example nerves connected to the vocal cord muscles, with a nerve stimulator, and to electronically evaluate, or view on a video monitor, the muscle electrical responses, thereby giving the surgeon an indication of the location and physiologic integrity of these nerves during performance of a surgical procedure. This is particularly useful in Thyroidectomy and Para-thyroidectomy operations. In addition, laryngeal monitoring has been found to be of clinical value in certain neurosurgical and orthopedic surgical procedures such as Anterior Cervical Discectomy and Posterior Fossa Craniotomy. Also, with prolonged intubation and airway ventilator support, such as is provided in an intensive care unit for certain medical conditions, such as chest trauma, pneumonia, or chronic lung disease, medical practitioners would benefit from being able to evaluate laryngeal electromyography on an ongoing basis to evaluate the depth of sedation and the patient's status to determine if the airway support is still required or whether the endotracheal tube can be removed.
Currently, it is common practice to monitor laryngeal electromyography using laryngeal electrodes (the electrical signal pickup surfaces used to collect the muscle signals) which are either adhesively secured to the surface of the endotracheal tube or are embedded into the tube surface during the manufacture of the endotracheal tube. Both of these methods involve the addition of components to the endotracheal tube which are not commonly incorporated into this device such as metallic plates, adhesives, lead wires, and structural elements resulting in raised portions on the smooth physical profile of the endotracheal tube surface. Additionally, these devices can also introduce structures into the vicinity of the larynx and can cause injury to the vocal cords. For these reasons, the manufacturers of all currently available laryngeal surface electrodes do not recommend continuous laryngeal electrode placement for monitoring purposes in excess of eight hours. The surgeon and anesthesiologist are therefore required to remove the dedicated endotracheal tube with attached electrode and reintubate the patient with a standard, non-electrode endotracheal tube prior to moving the patient to the recovery room or ICU for prolonged respiratory support. This entails the risk of a separate, second airway manipulation and deprives the physician of valuable information which is provided by prolonged and continuous laryngeal monitoring.
Additionally, because the components of the electrodes in current embodiments of attachable or integrated endotracheal tube electrodes are different in structure and type to standard endotracheal tube components, they create a zone of stiffness that does not allow, or retards, flexing of the endotracheal tube when placed in its desired position, namely in a semi S-curve configuration extending for the length of the electrode element. By constructing the part of the endotracheal tube electrode that is inside the patients mouth, pharynx, and larynx using components which are flexible, rather than rigid, such as described herein below, the endotracheal tube electrode are located for optimal signal collection and minimal negative effects on the surrounding laryngeal tissue, subject to other constraints caused by the other materials used to form the laryngeal tube.